(1) Field of the Invention
The present invention relates to a four-way switching valve, and more particularly to a four-way switching valve that carries out switching of refrigerant pipes e.g. in a heat pump-type heating and cooling system for an automotive vehicle when the operation mode is switched between heating and cooling operation modes.
(2) Description of the Related Art
In a heating and cooling system for an automotive vehicle, a refrigerating cycle is employed during cooling operation, and engine coolant is used as a heat source during heating operation. Recently, however, due to the improvement in combustion efficiency of the engine, the temperature of the coolant does not rise high enough to obtain sufficient heating temperature in winter. For this reason, there is an increasing demand for a system which can perform both cooling and heating. In a heating and cooling system of this kind, it is necessary to reverse the direction of flow of refrigerant flowing through an indoor heat exchanger and an outdoor heat exchanger, as the system is switched between cooling and heating operations. It is a four-way switching valve that performs switching the direction of flow of the refrigerant.
A four-way switching valve of this type is known which switches a refrigerant passage by causing a cup-shaped valve element to slide (see e.g. Japanese Unexamined patent Publication (Kokai) No. H07-151251 (Paragraph numbers [0035] to [0036], FIG. 3)). This four-way switching valve includes a port for introducing discharge pressure from a compressor, three ports formed side by side such that they open in the same plane, and the cup-shaped valve element for causing two of the three ports to communicate with each other and the remaining one to communicate with the port for introducing discharge pressure. One of the three ports disposed in the center is connected to the suction side of the compressor, and the other two thereof are connected to an indoor heat exchanger and an outdoor heat exchanger, respectively. Pistons are disposed on opposite sides of the valve element in the sliding direction, for actuating the valve element to cause the same to slide on the same plane where the three ports open, and selection control is provided such that a pilot valve introduces high pressure via a tube from the port for introducing high pressure selectively into operating chambers of the pistons, and one of the operating chambers into which the high pressure is not introduced is connected to the port connected to the suction side of the compressor.
With the arrangement of the four-way switching valve, when the pilot valve is in a certain switching position, the discharge pressure is introduced into the operating chamber of one piston via the tube, and the operating chamber of the other piston is connected to the suction side of the compressor via a tube, whereby the one piston actuates the valve element to cause two of the ports formed side by side, which are remote from the one piston, to communicate with each other, and at the same time cut off these two ports from the discharge pressure, and the remaining one of the ports to communicate with the port for introducing the discharge pressure. As a consequence, the cooling and heating system is formed with a refrigerant path along which the refrigerant delivered from the compressor flows to the compressor via the port for introducing the discharge pressure, one of the ports which is not covered with the valve element, a first heat exchanger, an expansion device, a second heat exchanger, and two of the ports which are connected by the valve element, causing the first heat exchanger to perform condensing of the refrigerant and the second heat exchanger to perform evaporation of the refrigerant, whereby the system performs cooling operation by the second heat exchanger.
Inversely, when the pilot valve is in the other switching position, the operating chamber of the one piston is connected to the suction side of the compressor via the tube therefor, and the discharge pressure is introduced into the operating chamber of the other piston, whereby the other piston actuates the valve element to cause two of the ports formed side by side, which are remote from the other piston, to communicate with each other and at the same time be cut off from the discharge pressure, and one of the ports closest to the other piston to communicate with the port for introducing the discharge pressure. As a consequence, the cooling and heating system is formed with a refrigerant path along which the refrigerant delivered from the compressor flows to the compressor via the port for introducing the discharge pressure, one of the ports which is not covered with the valve element, the second heat exchanger, the expansion device, the first heat exchanger, and two of the ports which are connected by the valve element, causing the second heat exchanger to perform condensing of the refrigerant and the first heat exchanger to perform evaporation of the refrigerant, whereby the system performs heating operation by the second heat exchanger.
However, the conventional four-way switching valve performs the switching of ports by sliding of the valve element, and therefore, a resilient sealing material cannot be used for sliding parts, which degrades the sealability of the four-way switching valve.
Further, the valve element has a structure in which the high discharge pressure is applied to the outside thereof and the low suction pressure is applied to the inside thereof, so that when the switching of ports is carried out when the difference between the high discharge pressure and the low suction pressure is large, the valve element is slid while being pressed against the siding surface by the discharge pressure so that the switching of ports cannot be performed smoothly, sometimes causing unusual noise, such as a snagging sound, to be generated when the valve element passes the openings of the ports.
Further, it is necessary to implement the pressure passages by tubes, for enabling the pilot valve to make high or low the pressure in the operating chamber of each piston that actuates the valve element, which increases the number of component parts and the number of manufacturing steps, and complicates the construction of the valve.